The present invention relates generally to methods for biologically treating wastewaters, contaminated groundwaters or the like, and more particularly to an improved process for treatment and disposal of wastewater generated from manufacture, processing or disposal of ammonium perchlorate materials and remediation of perchlorate contaminated groundwater or soil washwater.
Class 1.1 rocket motor propellants typically contain about 14% ammonium perchlorate, 14% HMX and 30% nitroglycerine as oxidizers, 20% aluminum fuel and 22% nitrocellulose binder. Class 1.3 propellants typically contain 70% ammonium perchlorate oxidizer, 17% aluminum fuel and 13% PBAN binder. Large amounts of wastewater containing 10% or more by weight of ammonium perchlorate may be generated from propellant manufacture or processing or from rocket motor washout operations.
Prior methods for disposal of ammonium perchlorate based propellants generally consisted of open fuel burning or static firing of fueled rocket motors. Uncontrolled open burning may result in the spread of combustion products or unexploded material to areas surrounding the burn site and therefore represents a source of contamination for soil and groundwater. Open burning and static motor firing result in the release to the environment of large amounts of hydrogen chloride, nitrogen oxides and unburned hydrocarbons, and are considered environmentally unacceptable disposal methods.
Prior art processes for treatment of industrial wastewaters include U.S. Pat. No. 3,755,156 to Yakovlev et al, entitled "Method for Biological Treatment of Industrial Waste Water," describing the biochemical reduction of chromium or chlorine inorganic oxygen containing compounds in industrial wastewaters by mixing the wastewaters with municipal sewage having a biological oxygen demand (BOD) which exceeds the amount of oxygen in the inorganic chromium and chlorine oxides. The combined wastewaters, municipal sewage and recycled acclimated sludge are held under anaerobic conditions with the bioreduction of perchlorates occurring at volumetric rates of about 12 mg ClO.sub.4.sup.- /hr per liter. The treated wastewater is then passed to an aeration chamber for further reduction of BOD. U.S. Pat. No. 3,943,055 to Korenkov ct al, entitled "Process for Purification of Industrial Waste Waters from Perchlorates and Chlorates," describes the controlled addition of the microorganism Vibrio dechloraticans Cuznesove B-1168 to a mixture of perchlorate or chlorate bearing industrial wastewater and municipal sewage with the bioreduction of those compounds to chloride salts.
The process described in U.S. Pat. No. 5,302,285 to Attaway et al, entitled "Propellant Wastewater Treatment Process" (herein referred to as Attaway '285), provided a substantial improvement to the then existing art by providing a two-stage anaerobic-aerobic process for the biological reduction of wastewater containing ammonium perchlorate. Wastewater treatment according to Attaway '285 included the steps of reducing perchlorate to chloride in a first stage anaerobic reactor using a mixed bacterial culture containing a specific unique microorganism HAP1, which uses perchlorate as its terminal acceptor, under controlled pH, nutrient and temperature conditions, followed by reduction in a second stage aerobic reactor of the organics produced in the anaerobic reactor to carbon dioxide and sludge, the effluent liquid being disposable to a conventional sanitary sewer system. The Attaway '285 process resulted in reduction of perchlorate wastewater concentrations as high as 7750 mg per liter (about a 26 fold improvement over the prior art); HAP1 demonstrated a specific degradation rate of at least 1492 mg ClO.sub.4.sup.- /hr per gram of dry biomass (about a 21 fold improvement over the prior art); the process demonstrated continuous volumetric degradation rate at least 2-fold higher (221 mg ClO.sub.4.sup.- /hr per liter) than the prior art at 10-fold higher perchlorate concentrations (3000 mg per liter).
The invention is a significant improvement over Attaway '285 and comprises treatment of propellant wastewaters with specific nutrient additions in a novel anaerobic gaslift bioreactor to reduce perchlorate to chloride and nitrate to nitrogen. The gaslift reactor is populated with a mixed bacterial consortium including HAP1 as the primary component. The liquid in the reactor is sparged with hydrogen gas which serves as the biochemical reductant for reducing perchlorate. Tandem use of this specific nutrient composition in a hydrogen rich environment allows an increase in the ratio of the perchlorate reducing bacterium HAP1 to other non-perchlorate reducing members of the consortium and provides unexpectedly higher efficiency for perchlorate reduction. In the process of the invention, the required nutrient quantities are significantly less than required in Attaway '285, and the chemical oxygen demand (COD), solids and sludge produced in the anaeribic process are greatly reduced as compared to the Attaway '285 process.
It is therefore a principal object of the invention to provide a process for treatment and disposal of industrial wastewaters.
It is another object of the invention to provide an improved process for treatment and disposal of wastewater containing perchlorate-based materials.
It is another object of the invention to provide an economical and environmentally safe process for biotreatment of wastewaters containing perchlorate-based materials resulting from rocket motor washout processes, or of perchlorate-contaminated soils or groundwater.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.